全文获取类型
收费全文 | 978篇 |
免费 | 69篇 |
国内免费 | 90篇 |
专业分类
化学 | 739篇 |
晶体学 | 4篇 |
力学 | 47篇 |
综合类 | 77篇 |
数学 | 51篇 |
物理学 | 219篇 |
出版年
2023年 | 8篇 |
2022年 | 24篇 |
2021年 | 88篇 |
2020年 | 49篇 |
2019年 | 50篇 |
2018年 | 23篇 |
2017年 | 37篇 |
2016年 | 44篇 |
2015年 | 36篇 |
2014年 | 44篇 |
2013年 | 86篇 |
2012年 | 54篇 |
2011年 | 49篇 |
2010年 | 42篇 |
2009年 | 32篇 |
2008年 | 42篇 |
2007年 | 41篇 |
2006年 | 35篇 |
2005年 | 53篇 |
2004年 | 34篇 |
2003年 | 39篇 |
2002年 | 27篇 |
2001年 | 20篇 |
2000年 | 20篇 |
1999年 | 21篇 |
1998年 | 14篇 |
1997年 | 17篇 |
1996年 | 10篇 |
1995年 | 15篇 |
1994年 | 17篇 |
1993年 | 9篇 |
1992年 | 10篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 1篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1959年 | 3篇 |
排序方式: 共有1137条查询结果,搜索用时 46 毫秒
91.
植物生理信息采集处理系统研究 总被引:1,自引:0,他引:1
王成 《新疆大学学报(理工版)》2003,20(3):308-313
以虚拟仪器理论为基础研制的植物生理信息采集处理系统.应用了传感器技术、自动测量技术、微计算机软硬件技术及数据的数学处理方法.植物生理信息采集处理系统由传感器、信号调理电路、数据采集卡、通用计算机和数据采集软件、数据处理软件构成,实现了植物生理信息多通道数据的实时自动采集和处理功能.系统具有测量集成、植株活体无损测量、信息数字化、全自动记录、用数据库管理数据等特点. 相似文献
92.
93.
胡萝卜悬浮培养细胞和原生质体的玻璃化法超低温保存 总被引:7,自引:1,他引:6
采用玻璃化法成功地超低温保存了胡萝卡悬浮培养细胞及其原生质体,存活率分别为83.3%(TTC法检测)和47%(RDA法检测)。冻后细胞能恢复生长并再生植株。分析了玻璃化法超低温保存植物悬培养浮细胞和原生质体的主要影响因素。 相似文献
94.
Cytoskeletal involvement in cotton fiber growth and development 总被引:1,自引:0,他引:1
Robert W. Seagull 《Micron (Oxford, England : 1993)》1993,24(6):643-660
The organization of cellulose microfibrils in plant cell walls influences physical properties of the wall and thus cell expansion characteristics. Developing cotton fiber represents an excellent model system for the analysis of the biological regulation of cell wall patterns. Current research indicates that the cytoskeleton has a major role in directing the deposition and organization of cellulose microfibrils in the cell walls of many plant systems, including developing cotton fibers. Both microtubules and microfilaments appear to be involved in regulating changes observed in microfibril patterns during fiber development. The polylamellate architecture of the fiber wall can be attributed to changes in the orientation of cytoplasmic microtubules which appear to direct the orientation of microfibril deposition in each successive layer of the fiber wall. In the drug-induced absence of microtubules, cellulose is deposited in the fiber wall in a swirled pattern of bundled microfibrils. Interaction between adjacent microfibrils may influence cell wall organization on a localized level. In contrast to the direct involvement of microtubules on wall organization, microfilaments appear to be indirectly involved in the deposition of cellulose microfibrils. Current evidence indicates that microfilaments influence wall organization by controlling changes in microtubules patterns. Although a greater understanding of the relationship between the cytoskeleton and the fiber wall is needed, there is sufficient evidence to indicate that genetic manipulation of cytoskeletal components is one path toward future direct manipulation of cell expansion characteristic in many plant systems and may lead to improvements in the textile qualities of cotton fibers. 相似文献
95.
District heating plants are becoming more common in European cities. These systems make it possible to furnish users with warm water while locating the production plants in the outskirts having the double benefit of lowering the impact of pollution on the center of the city and achieving better conversion performances. In order to amortize the costs throughout the year, the system often includes a combined heat and power (CHP) plant, to exploit the energy during the summer as well, when the demand for warm water decreases. A linear programming model for the optimal resource management of such a plant is presented and some results for a real case are reported. A distribution network design problem is also addressed and solved by means of mixed integer linear programming. 相似文献
96.
Extraction of fullerene-containing carbon soots with various organic solvents has been studied at room temperature. Yields and compositions of toluene-soluble carbon soot fractions have been determined. Extracts of different carbon soot samples treated according to the toluene—trichlorobenzene—nitrobenzene scheme are studied.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1223–1225, July, 1995.The authors are grateful to E. B. Yagubskii and I. S. Krainskii for helpful discussion and help in the work.The work was financially supported by the Russian Foundation for Basic Research (Project No. 93-03-18705). 相似文献
97.
玉帘不同外植体培养,诱导出胚性、中间型和非胚性3种类型的愈伤组织,并再生植株.由胚性愈伤组织与叶肉细胞分离出原生质体,进行培养,启动了细胞分裂并形成了多细胞团.同时,还研究了影响玉帘组织培养以及原生质体分离和培养的诸因素. 相似文献
98.
通过对氢化-1,3,5-均三嗪-2,4-二酮衍生物抗病毒活性QSAR计算,预测标题化合物具有较好抗病毒活性,由氢化-1,3,5-均三嗪-2,4-二酮、丙烯酸甲酯和乙二醇衍生物经三步反应合成这些化合物,新化合物经^1H NMR,IR,MS确认结构。 相似文献
99.
Determination of Soot Particle Size in a Premixed Flame: a Static and Dynamic Light Scattering Study
Gert Kroner Heribert Fuchs Reinhard Tatschl Otto Glatter 《Particle & Particle Systems Characterization》2003,20(2):111-123
In this contribution we report upon our static and dynamic light scattering experiments to characterize soot particles in flames. We studied sooting laminar premixed flame with acetylene as fuel mixed with air as oxidizer. The air equivalence ratio of the combustion was larger than one. We used a Kaskan type burner with circular geometry and a stabilizing flow of nitrogen around the flame. We focused on the determination of the size of the soot particles in the center of the flame as a function of height above burner. In addition we investigated the influence of the mixing ratio of the gases on the size of the particles. Our results show that static light scattering is better suited than dynamic light scattering for a fast and reliable characterization of soot particles in flames. The latter needs detailed a priori information about the flame to allow the unique determination of sizes from the diffusion measurements. The soot particles grow monotonously with height above burner and with decreasing air equivalence ratio. The aggregates have a fractal dimension lower than two. 相似文献
100.
Summary A method was developed for the determination of nitrobenzoic acids and nitrophenols as well as of diaminoaromatics and was
applied to the analysis of water samples from the former ammunition plant at Elsnig (Saxony, Germany).
The procedure is based on a preseparation into a neutral, an acidic and a basic fraction by multi-step extraction at different
pH values followed by HPLC analysis with UV and electrochemical detectors, coupled in series.
Applying optimized enrichment conditions, all investigated compounds were extracted from spiked distilled water with recoveries
>80% and variation coefficients <7%. Similar results were obtained with spiked ground water samples.
After enrichment, all compounds can be analysed by HPLC with UV detection at concentrations below 100 ngL−1. The electrochemical detector (ELCD) allowed a selective and sensitive detection of the nitrophenols and especially of the
diaminoaromatics and, therefore, provides, some advantages in the analysis of real samples.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996 相似文献